I *finally* got around this weekend to installing my 100 cps cat and RRE stealth exhaust (still using the stock DP). Took the car out for a test drive and didn't notice much difference in performance, but then I looked at the log data and found a big difference there. Apparently the new exhaust pieces greatly reduced back pressure, and in order to keep the same boost levels, the direct boost control system had to pull out a ton of WGDC at higher rpm. It was pretty cool to see the new logs for the first time and realize how well the ECU maintained the target boost level with such a drastic change in exhaust pressure.

Anyhow, I'll need to retune the BWGDC curve soon so that things work as expected anytime I punch the throttle.

Random Tech HFC and stock cat-back: Here you can see that the WGDC is pretty much following the BWGDC curve exactly.



100 cps cat and RRE stealth: Here you can see how much WGDC is being pulled back from the BWGDC curve to maintain the target boost levels.

 

Very nice. What correction delay are you using?

 

Cool stuff but how how come the boost error isn't changing very much as well?

EDIT: Nevermind now I see it.

 

Others might have this question as well ...

It's because the boost is correct. The WGDC is what has changed. The boost error value is the comparison of desired boost to actual, which are both still very close in this situation.

 

Correction delay = 1. It took me a while to come around to the idea that the shortest correction delay was best. Its necessary to zero out the first few "undershoot" correction values though in the WGDC correction table. Otherwise, the short correction delay can induce momentary overshoot on spool up.

 

What are your initial impressions on the cat (and new cat-back)?

 

awesome stuff;

Yes lots of small changes are better than fewer big changes.

 

off-topic: do u guys think we should modify the waste gate in order to get the best out of the turbo or a very small pill should do the trick???


mrfred, up until which error% should you zero out in the wgdc error correction table?? ie: over 10% error should be zero???



Rgds+

 

Wow that is surprising from just a cat and catback.

 

Both. The stock boost solenoid doesn't seem to be able to flow air away from the WG with enough volume to let the WG hold full tension at high RPM.

The solution is to upgrade the solenoid or add a smaller pill to let the WG hold full tension at high RPM, and then to upgrade the WG actuator if stock tension isn't enough for you. Both methods work and they work even better together.

 

Yeah, the boost error never gets really big, except perhaps at 5000 rpm where it gets up to around 1-1.5 psi. Its because the BWGDC curve still has the correct general shape, but progressively runs too high as the rpms increase (caused by the decreased exhaust back pressure improving turbo efficiency).

 

Here is my current correction table:

 

mrfred, are you using the GM or stock BCS? and if stock what pill?

 

- Stock BCS
- Stock pill at the tee
- no pill at the BCS
- bleed hole (to atmosphere) in the boost hose just before the BCS

 

Great results!